YOGA AND ALCHEMY 213 the reader of this biography; some of them were relatives of Ho's, and a few of the stories were witnessed by him. This book, and the book on medical recipes bearing the names of Su Tungpo and Shen Kua as co-authors, gives some idea of the methods of treating cinnabar. Read- ing these stories and formulas, one gets the following impressions. There was always "a pill furnace". The alchemists worked with mercury, sulphur, copper, silver, arsenic compound, and nitrate, or salt- petre. It is possible that they also played with gold sulphide. Both mercuric sulphide (cinnabar) and gold sulphide form red pigments, and various mercury compounds were taken as medicine. In the in- accurate records of those days, popular tales credited various Taoists with the possession of a formula to transform copper into gold. It is £fertain that people had been able to produce a purple-red gold alloy, which was fashioned into various kinds of vessels, and made a profit for themselves. It is also possible that some Taoists rubbed mercury on copper and passed it on as silver to ignorant people. They made an amalgam of gold and mercury, which was an easy thing to do. They also combined sulphur with mercury, calling the product "yellow gold" and again, in the same sentence, "dead sulphur". There is a story that a monk was actually able to produce pure gold which passed the tests of the gold merchants of the capital. From the description Ho gives I am quite sure that the Taoist worked from gold ^re gravel and was able to extract pure gold from the alloy. The tricky part of it was that the priest described this gravel as a form of copper, so that the story of transmuting copper into gold was (quite exciting. He was able to demonstrate to a relative of Ho the transformation of some of this gravel into gold. He said that the gravel was copper and that he carried it in this form rather than as pure copper because it might be stolen when he was travelling. The ore was heated over a fire but would not melt. Then the priest dropped a little white powder into the pan and the result was pure gold. The monk's story was as follows: He and two friends had years ago decided to go each his own way and then meet again in a certain place after ten years. They were to go out and search for the "philosopher's stone", and when they met they were to share the secret. The man who discovered the formula and was now telling the story had become a monk instead of a rich merchant, and this was how it happened. When the three friends met at the appointed time, they compared the results of their search. The priest showed his friends that he had found a-good formula, but that the product still contained impurities. One of his friends told him that he had obtained a powder for removing impurities. By adding this powder, they were able to produce pure gold.